At the time of bundling plural sheets (referred to “a set of sheets”) printed by an image forming apparatus employing an electrophotographying system such as a copying machine and a printing machined and producing plural sets of sheets, it is desirable to stack sheets discharged from a sheet discharging section on a tray so as to be able to sort for each set of sheets.
Here, as a sorting device to sort sheets for each set of sheets (also referred to “a shifting device”), widely employed is a device to shift a tray in a direction perpendicular to the discharging direction of sheets by about 10 to 20 mm and to stack a set of sheets on the tray on the condition each set of sheets is positioned to be out of alignment from other sets of sheets.
Further, as an aligning device to align edge surfaces of each set of sheets, Japanese Patent Unexamined Publication No. 2006-206331 discloses to provide a shifting section to conduct a sorting operation by shifting a tray and a pair of arranging members (sheet aligning members) to conduct an arranging operation (an aligning operation) by sandwiching edge portions of discharged sheets. This patent publication discloses a technique to shift the sheet aligning member to two stop positions in which at the time of shifting the tray, the sheet aligning member is rotated around a supporting shaft being a center of rotation and shifted upward to a retracting position, and at the time of conducting an aligning operation, the sheet aligning member is shifted downward to an aligning position.
However, in the above patent publication, at the time of shifting, after the sheet aligning member was rotated and shifted to the retracting position, the tray is shifted in the shifting direction by a predetermined distance, and then a sorting operation is conducted. At the time of aligning sheets, the sheet aligning member is rotated and shifted downward from the retracting position to the aligning position. Therefore, since it needs a time for shifting upward and downward, there is fear that in the case of a high speed machine, a next sheet is discharged in the middle course that the sheet aligning member is shifting upward or downward, and it is worried that the alignment of sheets becomes poor.